In a standard guidance system for guided projectiles, the rotor of the guidance gyro is generally held off its bearings until after the projectile exits the gun tube. The rotor is then automatically moved onto its bearings and the spin control circuitry brings the rotor up to its design speed. The cage coil is then energized to align the spin axis of the rotor with the projectile longitudinal axis. At target acquisition when guidance begins, the precession coils move the gyro to look at the target and the cage coil is dropped out of the circuit. The guidance system generates pitch and yaw canard commands which are applied to the pitch and yaw servos to guide the projectile or missile toward the target. It is necessary to apply rate feedback to the canard commands in order to avoid endless hunting by the guidance system or oscillation at the natural frequency of the airframe.
Rate feedback is normally derived by an additional sensor apart from the guidance gyro. This sensor may be a rate gyro, a vibrating beam or "vyro", a gas jet flowing on a hot resistance bridge, or another type of rate sensor. These sensors add additional costs and complication to the electronics package. Another scheme uses the guidance gyro gimbal angle differentiated for rate feedback. Gimbal angle is sensed by potentiometers attached to the pitch and yaw gimbals. However, this potentiometer system introduces friction on the gimbals which is undesirable.